We have used Escherichia coli strains, which carry the gene encoding the uridylytransferase enzyme in a ColEl hybrid plasmid, to obtain elevated amounts of this protein. Strain JA200/plC 38-39, previously shown to produce uridylytransferase (UT) and uridylyl-removing (UR) enzymes at levels 25-fold those found in the wild type strain, was used to purify these two activities to homogeneity. Copurification of these two activities throughout the procedure indicated that the UT UR enzyme is bifunctional in nature. Molecular weight determination in polyacrylamide gels showed UT UR to be 110,000 in size. The enzyme is composed of a single subunit. Results from gel filtration and gel electrophoresis steps indicate the protein oligomerizes readily.